The other day as I started my car from a dead cold start, a weird vibration emitted from underneath the pedals. After about ten seconds or so, the vibration seemed to go away. When I cut the car off for about three seconds and turned it on, the vibration "seemed" to be there again, almost unnoticeable (at this point, maybe my mind was playing tricks on me), but went away completely. Any thoughts on what the problem is??

 

the heat shields on the exhaust might be loose from years of rust. that happened to mine. i just ripped them off.